Navigation systems for displaying a current vehicle position on a map have been widely adopted in vehicles. These navigation systems require map data. The map data for navigation systems are usually recorded in a data storage unit, for example, a CD-ROM or DVD, included in the navigation system. Regional map data are retrieved from the data storage unit as needed.
Recently, a separate server for providing map data through a wireless network has been used, such that the navigation system can receive regional map data from the server. The regional map data stored in the memory typically has the form of a grid, that is, the regional map is divided into a plurality of square cells. Map data in each cell is called “cell data” hereinafter.
Typically, the regional map data comprising a plurality of data cells which are selected around the current position of the vehicle is transmitted to the navigation system in the vehicle. Accordingly, in the case where the network load increases or the network speed decreases, renewal of the regional map data is delayed. Therefore, it is preferable that the amount of data required to be transmitted is reduced to a minimum.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.